Electrically actuable ignitor for passenger restraint system employing an inflatable cushion

ABSTRACT

A reliable and inexpensive ignitor for rapidly &#39;&#39;&#39;&#39;firing&#39;&#39;&#39;&#39; the combustible gas-producing charge of an inflatable-cushion type safety apparatus for motor vehicles. The ignitor preferably comprises a modified AG 1/2 photoflash lamp assembly which has an open-ended glass tube instead of the sealed glass envelope normally employed and is devoid of shredded foil. The open end of the tube is sealed by a plastic diaphragm which ruptures when a predetermined amount of primer inside the tube is ignited by passing electric current through a wire filament that is embedded within the primer.

United States Patent [151 3,695,179 Rainone et a]. [451 Oct. 3, 1972[54] ELECTRICALLY ACTUABLE IGNITOR 2,333,725 11/ 1943 Kreidler ..431/94FOR PASSENGER RESTRAINT SYSTEM 3,351,015 11/1967 Wallack et a1..102/70.2 EMPLOYING AN INFLATABLE 3,490,855 l/ 1970 Buzalski ..431/95CUSHION Pri E Be ABo hlt ma xammernamin rc e [72] Inventors: Nicholas J.Rainone, Clifton; Jacob Assistzt Exam-"way. Doramus F. Mlchael Paramus,both of Attorney-A. T. Stratton, W. D. Palmer and D. S. Bu- [73]Assignee: Westinghouse Electric Corporation, leza P'tt b P l S urgh a 57ABSTRACT [22] Filed: Nov. 24, 1970 A reliable and inexpensive ignitorfor rapidly firing PP ,474 the combustible gas-producing charge of aninflatablecushion type safety apparatus for motorvehicles. The 52 us.Cl. ..102/7o.2 R, 180/103 AB, 431/95 Preferably a AG 511 int. Cl. ..F42c19/12, B60k 35/00 phtflash l assembly Much has [58] Field of Search102/70 2 180/103 glass tube instead of the sealed glass envelope nor-/53 1 bl/94 95 mally employed and is devoid of shredded foil. The openend of the tube is sealed by a plastic diaphragm which ruptures when apredetermined amount of [56] References Cited primer inside the tube isignited by passing electric UNITED STATES PATENTS current through a wirefilament that is embedded within the primer. 3,549,169 12/1970 Oldberg..180/103 3,332,257 6/ 1967 Gainer et a]. ..431/95 9 Claims, 5 DrawingFigures ELECTRICALLY ACTUABLE IGNITOR FOR PASSENGER RESTRAINT SYSTEMEMPLOYING AN INFLATABLE CUSHION BACKGROUND OF THE INVENTION 1 Field ofthe Invention This invention generally relates to an inflatablecushiontype safety system for motor vehicles and has particular reference to anignitor for triggering such a system by means of an electric current.

2. Description of the Prior Art Various safety devices utilizing rapidlyinflated bags or cushions for protecting the passengers of automobilesfrom injury during a collision are known and are presently beingevaluated. A passive restraint system of this type employing a flexibledual-chamber container that is rapidly inflated by a gas mixture isdisclosed in US. Pat. No. 3,476,402. A similar apparatus utilizing aninflatable cushion that is attached to a pressure container which isopened by detonating an explosive charge and wherein at least a portionof the cushion is made of porous material is disclosed in US. Pat. No.3,511,519.

In other systems the bag or cushion is inflated with gases generated bya charge of fulminating material such as a mass of an explosivelycombustible chemical. In order to be practical from both a functionaland cost standpoint, systems of this type require an ignitor which isnot only simple, inexpensive and reliable but one which will set off thegas-producing charge within the alotted time typically, a fewmilliseconds.

SUMMARY OF THE INVENTION The present invention provides an ignitor whichmeets all of the foregoing requirements. Briefly, the ignitor comprisesa component that is similar to a miniature electric lamp and can thus beactuated by a small electric current.

In accordance with a preferred embodiment the ignitor comprises amodified AG 1E photoflash lamp mount and bulb assembly. The tungstenfilament is coated with a large but controlled amount of a selectedthermally ignitable primer material and the sealed bulb is replaced witha tubular glass sleeve that is closed at one end by the usual press sealbut has its opposite end closed by a rupturable diaphragm of thinplastic. The ignitor, accordingly, has the same basic structuralfeatures as an AG photoflash lamp. Embryonic ignitor assemblies can thusbe efficiently and economically manufactured on the same high-speedmachines used to make such lamps. The subsequent operations required todeposit the proper amount of primer on the filament, form the rupturableplastic diaphragm, etc. can readily be performed by automated equipment.

The present invention accordingly provides ignitors that can be massproduced in a manner which drastically reduces their unit cost andinsures the high degree of quality and uniformity necessary to meet thestringent reliability standards of the safety system in which they willbe used. The ignitors are hermetically sealed and will thus remain freshand ready for use over long periods of time. They are also very ruggedand will withstand the various vibrational forces, etc. encountered inthe cars and other vehicles in which they are installed.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be obtained from the exemplary embodiment shown in the accompanyingdrawing, wherein:

FIG. 1 is a schematic elevational view, partly in cross-section, of aninflatable-cushion type safety apparatus which includes the electricalignitor component of the present invention;

FIG. 2 is an enlarged elevational view, partly in section, of theignitor component used in the apparatus shown in FIG. 1; and

FIGS. 3-5 are elevational views, mainly in cross-section, illustratingthe various operations required to complete the ignitor.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown asafety system 9 for an automobile or other vehicle which uses theinflatable cushion or bag concept for protecting passengers from injuryduring a crash. The system 9 includes the usual gas generator such as ametalcasing or bottle 10 that contains a charge 12 of a pyrotechnic typematerial that will ignite in an explosive-like manner and generate asufficient quantity of gas to rapidly inflate and deploy a flexible bag16 secured to the bottle. The gas-producing charge 12 is set off by anignitor 18 that is seated in a suitable socket 20 mounted in an openingin a wall of the bottle 10.

The ignitor 18 is so positioned that hot gases and incandescentparticles ejected from the ignitor will strike the gas-producing charge12 and set it off when the ignitor 18 is electrically energized. Thelatter is achieved by a pair of conductors 22 that are connected to avoltage source (the car battery for example) through a suitableelectromechanical sensor, such as an inertia or pendulum type switch,that instantaneously detects and is activated by a collision.

The present invention relates to the electrically actuable ignitor 18which fires the gas-producing charge 12 of the restraint system 9 andthis component and the manner in which it is manufactured will now bedescribed.

As shown in FIG. 2, the ignitor 18 comprises an elongated hollow body ofvitreous material, preferably a glass tube 24 of circular cross-sectionas illustrated, that is terminated at one end by a press seal 26 and hasits opposite end closed by a rupturable membrane or diaphragm 28 that issecured to the lip of the tube. While various types of diaphragrns 28may be used, in the preferred embodiment shown it consists of a thinfilm of a suitable plastic, such as that marketed by the Dow ChemicalCompany under the trade name Saran. The diaphragm 28 is protected fromphysical damage during handling, storage etc. by an overcoating 30 of asuitable plastic, such as cellulose acetate, that extends around theexterior side walls of the glass tube 24 and covers the adjacentportions of the press seal 26 of fused glass. The exterior plasticcoating 30 thus hermetically seals the ignitor l8 and also serves as aprotective sheath which holds the pieces of the shattered glass tube 24in place and prevents them from being propelled into the inflatable bag.16 and possibly causing it to rupture when the ignitor is actuated.

A pair of spaced conductors such as rigid lead-in wires 32 are embeddedin and extend through the press seal 26. A fine-wire filament 34 oftungsten or the like is attached to the inner ends of the lead-in wires32 and a suitable thermally ignitable primer 36 is disposed on thefilament 34. The amount of primer 36 required to achieve rapid ignitionof the gas-producing charge 12 is such that the primer materialcompletely encloses the filament 34 and the ends of the attached lead-inwires 32, as illustrated in FIG. 2. The exposed ends of the lead wires32 engage the contacts of the socket 20 and thus constitute theterminals of the ignitor 18.

To facilitate manufacture, medial portions of the lead-in wires 32 thatare located between the rigid body of primer 36 and the press seal 26are joined by a glass bead 38 thus providing a unitary mount that can bereadily handled and press sealed into the glass tube 24. The beadedmount and press seal features of the ignitor 18 are preferably identicalwith those employed in conventional AG 95 photoflash lamps and theignitors 18 can, accordingly, be manufactured in embryonic form on thesame high-speed machines presently being used to make such photoflashlamps.

An embryonic ignitor 18' produced by such a machine is shown in theright-hand portion of FIG. 3. As will be noted, it consists of theopen-ended glass tube 24 one end of which is formed into a press seal 26that encloses the end of a beaded mount consisting of the lead-in wires32 and conjoined glass bead 38 and tungsten filament 34. The firstoperation in completing the assembly of the ignitor consists of dippingthe end of the filament mount into a hardenable slurry or suspension ofprimer material. This can be achieved by lowering the embryonic ignitor18' into a cup 40 (as indicated by the arrow at the right of FIG. 3)which contains the primer suspension 41 and fits inside of the glasstube 24. Thus, only the filament 34 and inner ends of the leads 32 aredipped into the primer material 41. After the mount has been dipped asufficient number of times to deposit the proper amount of primer 36 onthe filament and leads, the ignitor assembly 18' is retracted from thecup 40, as indicated by the arrow at the left of FIG. 3. Of course, thedeposited primer is dried after each of the dipping operations.

The next operation consists of closing the open end of the embryonicignitor 18' with a rupturable diaphragm, which operation is shown in thesplit-view of the ignitor depicted in FIG. 4. As will be noted, thepartly fabricated ignitor 18 as received from the primer-dippingoperation is immersed with its open end downward as indicated in theright half of FIG. 4) into a shallow cup 42 that contains a solution ofa suitable hardenable plastic resin, such as the aforementioned Saran"plastic. The open end of the tube 24 is submerged to a depth sufficientto cause a thin film 28 of the plastic to be bonded to the rim of thetube after the assembly 18' is slowly retracted from the cup 42 and theadhered plastic has dried and rigidified, as indicated in the left halfof FIG. 4. As will be noted, the cup 42 is larger than the end of theglass tube 24 to permit free insertion and withdrawal of the latter.

The final step in the manufacture of the ignitor is shown in thesplit-view illustrated in FIG. and consists of dipping the assembly 18'produced by the previous operations into a vessel 44 that contains asolution of another plastic 45. This step is shown in the right half ofFIG. 5. As will be noted, the vessel 44 is of sufiicient depth and sizeto permit the entire ignitor assembly 18 to be immersed in the plasticsolution 45 approximately to the end face of the press seal 26. Afterthe assembly 18 has been withdrawn from vessel 44 and the adheredplastic has cured to form a protective coating 30 of substantiallyuniform thickness, as shown in the left half of FIG. 5, a completedignitor 18 of the type shown in FIG. 2 is provided.

SPECIFIC EXAMPLE Primer Composition Lacquer (2.7% solids mixture of 50cc nitrocellulose and amyl acetate) Powdered zirconium 50 gramsFinely-divided potassium perchlorate 29 grams Finely-divided anhydrousstrontium 29 grams nitrate The nitrocellulose serves as an organicbinder which holds the hardened primer material in place on the end ofthe mount. In the above formulation, the potassium perchlorate,strontium nitrate and powdered zirconium are present in stoichiometricamounts and such amounts are preferred in order to achieve primerignition in a minimum amount of time. From approximately milligrams to l15 milligrams of primer 36 were coated over the filament 34 and innerends of the lead wires 32. Tests have shown that 100 milligrams of theaforesaid primer formulation will ignite within 4 milliseconds after theignitor 18 has electrically energized.

The plastic diaphragm 28 was formed by dipping the end of the embryonicignitor 18' approximately 2 millimeters into a solution consisting of 10cc of methyl ethyl ketone and 2.5 grams of F-3l0 Saran powder (marketedby the Dow Chemical Company). Saran is the trade name for a resinconsisting of a copolymer of vinylidene chloride and vinyl chloride.

The protective plastic coating 30 was formed by dipping the embryonicignitor 18 into a solution consisting of 21.9 percent by weightcellulose acetate in a suitable solvent such as a mixture of acetone andvarious alcohols. Such solvents are well known in the photoflash lampart.

While zirconium, potassium perchlorate and strontium nitrate have beenspecified in the aforementioned formulation, the invention is notlimited to these materials. The primer can, accordingly, comprise anysuitable mixture of an oxidizer and a fuel. The fuel can comprise anysuitable powdered incandescible metal, such as magnesium or the like, ora mixture of such metals. The primer can also contain bulk materials(such as iron filings, larger magnesium particles and glass powder)which will carry the heat from the ignited primer 36 to the charge 12 ofgas-producing material and thus further minimize the time required toactivate the restraint system 9 and inflate and deploy the bag 16.

We claim as our invention:

1. An electrically actuable ignitor adapted for use in a passengerrestraint system having an inflatable cushion, said ignitor comprising;

a rigid hollow body of electrically non-conductive material that isclosed at one end by a diaphragm and has a seal at its opposite endthrough which a pair of spaced conductors extend,

a wire filament fastened to the inner ends of said conductors, and

a primer comprising a quantity of thermally ignitable combustiblematerial disposed on at least a portion of said filament,

said diaphragm having a wall thickness less than that of said hollowbody and thereby constituting an end closure that ruptures when saidignitor is actuated.

2. The ignitor according to claim 1 wherein; said rigid hollow body iscomposed of frangible vitreous material, and

the walls of said hollow vitreous body are covered by an exterior layerof plastic that encloses and constitutes a protective sheath for saidvitreous body.

3. The ignitor according to claim 1 wherein said primer comprises amixture of a fuel and an oxidizer.

4. The ignitor according to claim 3 wherein said fuel comprises apowdered incandescible metal and said oxidizer comprises admixedpotassium perchlorate and strontium nitrate.

5. The ignitor according to claim 4 wherein said powdered incandesciblemetal is a metal selected from the group consisting of zirconium,magnesium, and mixtures thereof.

6. The ignitor according to claim 1 wherein; said rigid hollow bodycomprises a glass tube, said seal comprises a press seal formed at theend of said glass tube, said conductors comprise a pair of lead-inwires, said primer encloses the filament and the associated segments ofsaid lead-in wires but only partly fills the glass tube, said diaphragmcomprises a film of plastic material that is bonded to the rim of saidglass tube, and a protective coating of plastic covers the outersurfaces of said plastic diaphragm and glass tube, including theadjacent portions of the press seal, and thereby constitutes a hermeticenclosure for the ignitor. 7. The ignitor according to claim 6 wherein;said filament comprises a fine tungsten wire, said lead-in wires arejoined by a glass bead that is located between the press seal and theinner ends of said wires, and said glass tube, lead-in wires, bead andfilament comprise an AG type photoflash lamp mount assembly. 8. Theignitor according to claim 7 wherein said primer comprises from about tomilligrams of a mixture of potassium perchlorate, strontium nitrate, a

inder and a powdered inc descible metal selected rom the groupconsisting cii zircomum, magnesium, and mixtures thereof.

9. The ignitor according to claim 8 wherein; said protective plasticcoating comprises a layer of cellulose acetate, said binder comprisesnitrocellulose, and said primer contains stoichiometric amounts ofpotassium perchlorate, strontium nitrate and powdered zirconium.

1. An electrically actuable ignitor adapted for use in a passengerrestraint system having an inflatable cushion, said ignitor comprising;a rigid hollow body of electrically non-conductive material that isclosed at one end by a diaphragm and has a seal at its opposite endthrough which a pair of spaced conductors extend, a wire filamentfastened to the inner ends of said conductors, and a primer comprising aquantity of thermally ignitable combustible material disposed on atleast a portion of said filament, said diaphragm having a wall thicknessless than that of said hollow body and thereby constituting an endclosure that ruptures when said ignitor is actuated.
 2. The ignitoraccording to claim 1 wherein; said rigid hollow body is composed offrangible vitreous material, and the walls of said hollow vitreous bodyare covered by an exterior layer of plastic that encloses andconstitutes a protective sheath for said vitreous body.
 3. The ignitoraccording to claim 1 wherein said primer comprises a mixture of a fueland an oxidizer.
 4. The ignitor according to claim 3 wherein said fuelcomprises a powdered incandescible metal and said oxidizer comprisesadmixed potassium perchlorate and strontium nitrate.
 5. The ignitoraccording to claim 4 wherein said powdered incandescible metal is ametal selected froM the group consisting of zirconium, magnesium, andmixtures thereof.
 6. The ignitor according to claim 1 wherein; saidrigid hollow body comprises a glass tube, said seal comprises a pressseal formed at the end of said glass tube, said conductors comprise apair of lead-in wires, said primer encloses the filament and theassociated segments of said lead-in wires but only partly fills theglass tube, said diaphragm comprises a film of plastic material that isbonded to the rim of said glass tube, and a protective coating ofplastic covers the outer surfaces of said plastic diaphragm and glasstube, including the adjacent portions of the press seal, and therebyconstitutes a hermetic enclosure for the ignitor.
 7. The ignitoraccording to claim 6 wherein; said filament comprises a fine tungstenwire, said lead-in wires are joined by a glass bead that is locatedbetween the press seal and the inner ends of said wires, and said glasstube, lead-in wires, bead and filament comprise an AG 1/2 typephotoflash lamp mount assembly.
 8. The ignitor according to claim 7wherein said primer comprises from about 100 to 115 milligrams of amixture of potassium perchlorate, strontium nitrate, a binder, and apowdered incandescible metal selected from the group consisting ofzirconium, magnesium, and mixtures thereof.
 9. The ignitor according toclaim 8 wherein; said protective plastic coating comprises a layer ofcellulose acetate, said binder comprises nitrocellulose, and said primercontains stoichiometric amounts of potassium perchlorate, strontiumnitrate and powdered zirconium.